cmake: Run clang-tidy incrementally in parallel

4 files changed, 132 insertions, 15 deletions

diff --git a/backend/CMakeLists.txt b/backend/CMakeLists.txt
index fcd75a8..2701c08 100644
--- a/backend/CMakeLists.txt
+++ b/backend/CMakeLists.txt
@@ -46,6 +46,10 @@ option(RCC_BACKEND_WARNINGS_AS_ERRORS "Treat compiler warnings as errors" OFF)
 option(RCC_BACKEND_ENABLE_CLANG_TIDY "Run clang-tidy during each compilation" OFF)
 option(RCC_BACKEND_ENABLE_EH "Enable C++ exception handling" OFF)
 option(RCC_BACKEND_ENABLE_RTTI "Enable C++ run-time type information" OFF)
+set(RCC_BACKEND_TIDY_BASE "HEAD" CACHE STRING
+    "Git revision used as the merge base for incremental clang-tidy")
+set(RCC_BACKEND_TIDY_JOBS "0" CACHE STRING
+    "Parallel clang-tidy jobs; zero uses the logical CPU count")
 
 if(RCC_BACKEND_ENABLE_EH AND NOT RCC_BACKEND_ENABLE_RTTI)
   message(FATAL_ERROR "RCC Backend exception handling requires RTTI")
diff --git a/backend/cmake/modules/RCCBackendBuild.cmake b/backend/cmake/modules/RCCBackendBuild.cmake
index 52e3a71..9ecc41b 100644
--- a/backend/cmake/modules/RCCBackendBuild.cmake
+++ b/backend/cmake/modules/RCCBackendBuild.cmake
@@ -13,6 +13,18 @@ function(rcc_backend_initialize_toolchain)
     NAMES "clang-tidy-${RCCBackendClangMajor}" clang-tidy
     REQUIRED
   )
+  find_program(
+    RCC_BACKEND_CLANG_TIDY_DIFF
+    NAMES clang-tidy-diff.py
+    HINTS "/usr/lib/llvm-${RCCBackendClangMajor}/share/clang"
+    REQUIRED
+  )
+  find_program(
+    RCC_BACKEND_RUN_CLANG_TIDY
+    NAMES "run-clang-tidy-${RCCBackendClangMajor}" run-clang-tidy
+    REQUIRED
+  )
+  find_program(RCC_BACKEND_GIT NAMES git REQUIRED)
 
   foreach(Tool IN ITEMS RCC_BACKEND_CLANG_FORMAT RCC_BACKEND_CLANG_TIDY)
     execute_process(
@@ -40,6 +52,9 @@ function(rcc_backend_initialize_toolchain)
 
   set(RCC_BACKEND_CLANG_FORMAT "${RCC_BACKEND_CLANG_FORMAT}" PARENT_SCOPE)
   set(RCC_BACKEND_CLANG_TIDY "${RCC_BACKEND_CLANG_TIDY}" PARENT_SCOPE)
+  set(RCC_BACKEND_CLANG_TIDY_DIFF "${RCC_BACKEND_CLANG_TIDY_DIFF}" PARENT_SCOPE)
+  set(RCC_BACKEND_RUN_CLANG_TIDY "${RCC_BACKEND_RUN_CLANG_TIDY}" PARENT_SCOPE)
+  set(RCC_BACKEND_GIT "${RCC_BACKEND_GIT}" PARENT_SCOPE)
 endfunction()
 
 function(rcc_backend_configure_target Target)
diff --git a/backend/cmake/modules/RCCBackendClangTidy.cmake b/backend/cmake/modules/RCCBackendClangTidy.cmake
new file mode 100644
index 0000000..16afeb4
--- /dev/null
+++ b/backend/cmake/modules/RCCBackendClangTidy.cmake
@@ -0,0 +1,83 @@
+# SPDX-License-Identifier: GPL-3.0-or-later
+
+foreach(Variable IN ITEMS RCC_TIDY_GIT RCC_TIDY_SOURCE_DIR RCC_TIDY_BINARY_DIR RCC_TIDY_BASE
+                          RCC_TIDY_JOBS RCC_TIDY_DIFF)
+  if(NOT DEFINED ${Variable} OR "${${Variable}}" STREQUAL "")
+    message(FATAL_ERROR "${Variable} is required for incremental clang-tidy")
+  endif()
+endforeach()
+
+execute_process(
+  COMMAND "${RCC_TIDY_GIT}" -C "${RCC_TIDY_SOURCE_DIR}" rev-parse --show-toplevel
+  RESULT_VARIABLE GitRootResult
+  OUTPUT_VARIABLE GitRoot
+  ERROR_VARIABLE GitRootError
+  OUTPUT_STRIP_TRAILING_WHITESPACE
+)
+if(NOT GitRootResult EQUAL 0)
+  message(FATAL_ERROR "cannot locate the Git worktree: ${GitRootError}")
+endif()
+
+file(RELATIVE_PATH TidyPath "${GitRoot}" "${RCC_TIDY_SOURCE_DIR}")
+if(TidyPath MATCHES "^\\.\\.")
+  message(FATAL_ERROR "backend source directory is outside its Git worktree")
+endif()
+
+set(DiffFile "${RCC_TIDY_BINARY_DIR}/CMakeFiles/rcc-backend-clang-tidy.diff")
+execute_process(
+  COMMAND "${RCC_TIDY_GIT}" -C "${GitRoot}" diff --no-ext-diff --unified=0 --merge-base
+          "${RCC_TIDY_BASE}" -- "${TidyPath}"
+  RESULT_VARIABLE DiffResult
+  OUTPUT_FILE "${DiffFile}"
+  ERROR_VARIABLE DiffError
+)
+if(NOT DiffResult EQUAL 0)
+  message(FATAL_ERROR "cannot produce incremental clang-tidy diff: ${DiffError}")
+endif()
+
+# git diff does not include untracked source files. Add their ordinary Git diff form so
+# LLVM's unchanged clang-tidy-diff.py driver checks new translation units before staging.
+execute_process(
+  COMMAND "${RCC_TIDY_GIT}" -C "${GitRoot}" ls-files --others --exclude-standard -- "${TidyPath}"
+  RESULT_VARIABLE UntrackedResult
+  OUTPUT_VARIABLE UntrackedFiles
+  ERROR_VARIABLE UntrackedError
+  OUTPUT_STRIP_TRAILING_WHITESPACE
+)
+if(NOT UntrackedResult EQUAL 0)
+  message(FATAL_ERROR "cannot list untracked clang-tidy files: ${UntrackedError}")
+endif()
+if(NOT UntrackedFiles STREQUAL "")
+  string(REPLACE "\n" ";" UntrackedFiles "${UntrackedFiles}")
+  foreach(UntrackedFile IN LISTS UntrackedFiles)
+    execute_process(
+      COMMAND "${RCC_TIDY_GIT}" -C "${GitRoot}" diff --no-index --no-ext-diff --unified=0 --
+              /dev/null "${UntrackedFile}"
+      RESULT_VARIABLE UntrackedDiffResult
+      OUTPUT_VARIABLE UntrackedDiff
+      ERROR_VARIABLE UntrackedDiffError
+    )
+    if(NOT UntrackedDiffResult EQUAL 0 AND NOT UntrackedDiffResult EQUAL 1)
+      message(FATAL_ERROR "cannot diff untracked file '${UntrackedFile}': ${UntrackedDiffError}")
+    endif()
+    file(APPEND "${DiffFile}" "${UntrackedDiff}")
+  endforeach()
+endif()
+
+execute_process(
+  COMMAND "${RCC_TIDY_DIFF}" -path "${RCC_TIDY_BINARY_DIR}" -p1 -quiet -j "${RCC_TIDY_JOBS}"
+  INPUT_FILE "${DiffFile}"
+  WORKING_DIRECTORY "${GitRoot}"
+  RESULT_VARIABLE TidyResult
+  OUTPUT_VARIABLE TidyOutput
+  ERROR_VARIABLE TidyError
+)
+set(TidyDiagnostics "${TidyOutput}\n${TidyError}")
+string(REGEX REPLACE "[0-9]+ warnings generated\\." "" TidyDiagnostics "${TidyDiagnostics}")
+string(STRIP "${TidyDiagnostics}" TidyDiagnostics)
+if(NOT TidyDiagnostics STREQUAL "")
+  message("${TidyDiagnostics}")
+endif()
+if(NOT TidyResult EQUAL 0 OR NOT TidyDiagnostics STREQUAL "")
+  message(FATAL_ERROR "incremental clang-tidy failed")
+endif()
diff --git a/backend/cmake/modules/RCCBackendDeveloperTools.cmake b/backend/cmake/modules/RCCBackendDeveloperTools.cmake
index 0313fe6..4c328f9 100644
--- a/backend/cmake/modules/RCCBackendDeveloperTools.cmake
+++ b/backend/cmake/modules/RCCBackendDeveloperTools.cmake
@@ -27,19 +27,34 @@ function(rcc_backend_add_developer_targets)
   if(TidyFiles)
     list(REMOVE_DUPLICATES TidyFiles)
 
-    # LLVM's repository runs clang-tidy-diff.py for changed lines. Keep the
-    # backend's explicit full audit deterministic by invoking clang-tidy once
-    # with the registered translation units instead of using a process pool.
+    # Match LLVM's normal lint path: pass the changed backend lines to its
+    # clang-tidy-diff.py driver, which runs independent translation units in parallel.
     add_custom_target(
       rcc-backend-tidy
       COMMAND
-        "${RCC_BACKEND_CLANG_TIDY}"
-        "--quiet"
+        "${CMAKE_COMMAND}"
+        "-DRCC_TIDY_GIT=${RCC_BACKEND_GIT}"
+        "-DRCC_TIDY_SOURCE_DIR=${RCC_BACKEND_SOURCE_DIR}"
+        "-DRCC_TIDY_BINARY_DIR=${CMAKE_BINARY_DIR}"
+        "-DRCC_TIDY_BASE=${RCC_BACKEND_TIDY_BASE}"
+        "-DRCC_TIDY_JOBS=${RCC_BACKEND_TIDY_JOBS}"
+        "-DRCC_TIDY_DIFF=${RCC_BACKEND_CLANG_TIDY_DIFF}"
+        -P "${CMAKE_CURRENT_FUNCTION_LIST_DIR}/RCCBackendClangTidy.cmake"
+      COMMENT "Running incremental clang-tidy on RCC Backend"
+      USES_TERMINAL
+      VERBATIM
+    )
+
+    add_custom_target(
+      rcc-backend-tidy-all
+      COMMAND
+        "${RCC_BACKEND_RUN_CLANG_TIDY}"
         "-p=${CMAKE_BINARY_DIR}"
-        "--warnings-as-errors=*"
-        ${TidyFiles}
-      COMMAND_EXPAND_LISTS
-      COMMENT "Running clang-tidy on RCC Backend"
+        -j "${RCC_BACKEND_TIDY_JOBS}"
+        -quiet
+        "-warnings-as-errors=*"
+        "${RCC_BACKEND_SOURCE_DIR}/.*"
+      COMMENT "Running full parallel clang-tidy audit on RCC Backend"
       USES_TERMINAL
       VERBATIM
     )
@@ -47,14 +62,14 @@ function(rcc_backend_add_developer_targets)
     add_custom_target(
       rcc-backend-analyze
       COMMAND
-        "${RCC_BACKEND_CLANG_TIDY}"
-        "--quiet"
+        "${RCC_BACKEND_RUN_CLANG_TIDY}"
         "-p=${CMAKE_BINARY_DIR}"
+        -j "${RCC_BACKEND_TIDY_JOBS}"
+        -quiet
         "-checks=-*,clang-analyzer-*"
-        "--warnings-as-errors=*"
-        ${TidyFiles}
-      COMMAND_EXPAND_LISTS
-      COMMENT "Running Clang Static Analyzer checks on RCC Backend"
+        "-warnings-as-errors=*"
+        "${RCC_BACKEND_SOURCE_DIR}/.*"
+      COMMENT "Running full parallel Clang Static Analyzer audit on RCC Backend"
       USES_TERMINAL
       VERBATIM
     )